Storage systems with a hierarchical structure are available in recent years, which incorporate high-speed storage media as a cache facility (or primary storage) together with less-expensive mass storage media as a back-end facility (or secondary storage). Hard disk drives (HDD) and solid state drives (SSD) are often used as primary storage, as are magnetic tape media as secondary storage. Such a hierarchical storage system is also called a virtual library system since it permits a host device to make virtual access to logical volumes in magnetic tape media via HDD or SSD.
Some virtual library systems employ a tape library device to store magnetic tape media containing produced logical volumes, in which a part of those logical volumes can be transported to or from a magnetic tape medium for the purpose of off-system storage. This act of transporting logical volumes is implemented by using, for example, the functions called “export” and “import.” The export function is to copy a plurality of logical volumes in the virtual library system to a single magnetic tape medium and eject the magnetic tape medium containing the copy. The import function is to load the local tape library device with a magnetic tape medium exported from other virtual library system, and reconstruct the foreign logical volumes for use in the local system.
FIG. 17 illustrates an export operation performed in a virtual library system. As can be seen from FIG. 17, a virtual library system is formed from a management server 710, a disk array device 720, and a tape library device 730, for example. The management server 710 controls operation of the disk array device 720 and tape library device 730 according to data read and write requests from a host device (not illustrated). The disk array device 720 includes a plurality of HDDs which serve as the primary storage. Specifically, in the example of FIG. 17, the disk array device 720 includes four HDDs 721 to 724. The tape library device 730 reads data from and writes data to magnetic tape, which is used as a portable data storage medium. The magnetic tape media in the tape library device 730 are used mainly as secondary storage.
The management server 710 creates logical volumes in the disk array device 720. Upon request from a host device, the management server 710 records given write data in a specified logical volume in the disk array device 720. The management server 710 also copies logical volumes from the disk array device 720 to magnetic tape media placed in the tape library device 730 at specified times. This act of copying logical volumes from the disk array device 720 to magnetic tape media is called, for example, “migrate.”
When a data read request is received from a host device, and if the requested data is part of a logical volume stored in the disk array device 720, the management server 710 reads the data out of the disk array device 720 and transmits it to the requesting host device. In the case where the logical volume containing requested data is absent in the disk array device 720, that logical volume is read out of a magnetic tape medium in the tape library device 730 and copied back to the disk array device 720. This act of copying a logical volume from a magnetic tape medium to the disk array device 720 is called, for example, “recall.” The management server 710 then reads the requested data out of the copied logical volume in the disk array device 720 and transmits it to the requesting host device.
When a host device requests export of logical volumes, each specified local volume is read out of the corresponding magnetic tape media and copied to the disk array device 720 for temporary use. The copied logical volumes are further copied from the disk array device 720 to a magnetic tape medium assigned for external storage purposes. That is, the export operation begins with recalling logical volumes back to the disk array device 720 and then executes migration to the magnetic tape medium for each specified logical volume, while using HDDs in the disk array device 720 as its work area.
To export, for example, a plurality of logical volumes distributed in magnetic tape media 731 to 733 as depicted in FIG. 17, a recall operation is first executed with each specified logical volume. That is, those logical volumes are copied temporarily from the magnetic tape media 731 to 733 to an HDD 724 in the disk array device 720. The copied logical volumes in the HDD 724 is then subjected to a migration operation, which copies them to a magnetic tape medium 734 for external storage purposes. When all specified volumes are copied, the tape library device 730 ejects the magnetic tape medium 734, thus finishing the export operation.
For example, some existing library devices with a media eject function are designed to enable a host to efficiently utilize I/O slots by using functional addresses to conduct virtual cartridge moves from storage slots to I/O slots. Some hierarchical storage systems with a media eject function are designed to form a set of storage media, so as to manage the mounting of storage media on a library device, as well as their ejection therefrom, on a medium set basis. Logical volumes are also managed in association with those sets of storage media. For example, the following literature describes such conventional devices and systems:    Japanese Laid-open Patent Publication No. 2006-163454    Japanese Patent No. 3630408    Japanese Laid-open Patent Publication No. 2006-172400
Referring again to the export procedure illustrated in FIG. 17, each of the specified logical volumes is subjected at least to a migration operation, and some of those logical volumes may also have to undergone a recall operation before migration. For this reason, it takes a long time from reception of an export command of a host device to ejection of a magnetic tape medium containing all specified logical volumes for external storage.